ORIGIN OF Cu2O PHASE PRESENT IN ANODE SLIMES - COPPER ANODE PASSIVATION STUDY (2ND REPORT).

An electrochemical technique, was adopted to investigate the origin of a Cu//2O phase often detected in the anode residues in copper electrorefining. It has been found that a Cu//2O phase in the slime layer originated from the surface of a corroding anode. Therefore, when oxygen content increases in the copper anode, an amount of Cu//2O entering the slime layer correspondingly increases; thus making it thicker. This causes the mass transport of Cu**2** plus ions from the surface of a corroding copper anode to be more restrictive, and, in turn, the tendency of the anode to passive increases. A Cu//2O phase present in a layer of anode slimes, when contacted with a sufficient amount of oxidizing agent such as dissolved oxygen, is expected to dissolve actively according to the chemical reaction, Cu//2O plus 2H//2SO//4 plus one-half O//2 yields 2 CuSO//4 plus 2 H//2O ( DELTA G degree equals minus 47. 3 kcal/mol) The addition of a small amount of H//2O//2 to Cu electrolyte increases the oxidizing effect, which agrees with the observed fact that the tendency of anodes to passivate dramatically decreases by this addition as well as by sparging O//2 gas in the electrolyte.